By Markland test, after a structural-geological surveying.

Corrado Cencetti

Dear Corrado Cencetti,

Thank you for your response. Let say, during a surveying I gathered 1000 datas. When I put it on the Markland Test, assume that It says a Wedge type of failure is expected due to intersection of joint sets and not individual joints. How can I possible know the exact location of this possible wedge that occured in the outcrop? Assume that you cannot determine it easly due to disintegrated and decompossed material.

Regards,

Bekir SF

It is impossible automatically.

Nevertheless, once fracture families have been identified, it is necessary to examine the possible wedges one by one

Thank you Corrado Cencetti for your valuable answer.

From the kinematic assessment alone you cannot, it only provides an indication of a potential to fail under the criteria of the assessment. The kinematic analysis only provides an indication of whether the different failure types could occur based on kinematics of the joint data collected. In the real, for failures to occur there will need to be other conditions that would allow failure to occur - for example, for planar failure to occur it may also require the presence of side release joints and joints which are sufficiently persistent. To determine whether failure is a real hazard you would need to go back to site and complete a subjective assessment based on engineering experience of the rock face, using the kinematic outcome as a baseline, to identify areas of increased risk where you would identify specific remedial measures such as spot or pattern bolting. Where the kinematic analysis indicates a risk of widespread instability that is unacceptable to the project, then you would design for the worse case and install a pattern of drains/bolts/dowels/mesh (etc)h to resist a defined case across the whole area. It is worth noting that there is often insufficient information to properly characterize the jointing at a particular location, especially in the third dimension, kinematic instability may be predicted by the kinetic assessment but that it is not observed, alternatively critical failure mechanism may not be indicated by the kinematic assessment due to insufficient information but are observed. Hope this helps

Dear Bekir,

the answers you received explain the complexity of the case you submit.

However, as you speak of a rocky mass disintegrated and decompossed I advise you:

- to take great care in defining the number of families of discontinuity that really govern the rock mass;

- define the shape and the dimensions of the VRU by identifying those with larger dimensions, for example. > 1-2 mc (those smaller, seldom give rise to individual slipping of wedges);

- identifying and delimiting in situ the homogeneous zones of disintegrated and decompossed rock masses and the individual large wedges;

- carry out the stability analysis with suitable and different methods for slipping wedges and disintegrated areas;

- in the stability analysis, also take into account the domino effect that can be generated due to the collapse of portions of disintegrated rock mass that can unlock the mobility of the rocky wedges.

I hope to be proved helpful.

Monitoring your slope using radar helps you to identify critical zones to focus on develop preventive actions or to alert risk to evacuate the area.

Study is based on statistic data so solution is probabilistic: you can't find the 'exact' location before. Anyway I suggest to focus on shapes you can see at slope surface. Concavities, planes, vertical planes can suggest explanation about type of failures.

Hope it helps.

Dear Steve Preedy , thank you for your answer. The last sentence you wrote is especially in my mind because It includes lots of uncertainity. Do you have any suggestions about how to deal with such a problem? Thanks.

Dear Giovanni Bruno , thank you also for your answer. Can you please expand the 3rd answer that you gave? Thanks.

Dear Carlos Mario Vargas Mendez , thank you for your answer. Which type of radar should I consider? e.g. terrestrial laser scanning, and did you mean to monitor the deformations with respect to time? Thank you.

Dear Filippo Forlani , thank you for your answer. How can I use a probabilistic solution to approach such a case? Thank you.

Dear Bekir, ther are software that helps you in this. Our company has one proprietary and can't be distributed.

You define a range for each variable (i.e. variation of dip/dipdirection of each family, possible water condition,variation of position of tension crack, and set the 'height of the solpe), then software (or excel) make many calculations. At the end you have a distribution of Safety Factor, the worst and worse wedges/plane/toppling failure found.

hope it helps.

Dear Filippo Forlani , as far as I know you meant using kind of limit equilibrium theory to define a factor of safety and graphing the results with various conditions with respect to the corresponding F’s. Then, the distribution will give the answer such as %10 probability of failure.

yes, and you can see the worse conditions found and understand (not locate) the most probable behaviour.

Some like pictures attached.

The in-situ delimitation of homogeneous rock masses can be done either visually or by drone photogrammetry.

Dear Filippo Forlani and Giovanni Bruno , many thanks for your contributions to my question.

Best Regards,

Bekir SF

I don't think using a probabilistic approach is the right thing to do. The most dangerous and statistically processed direction of cracks is not the same. The safety factor is very sensitive to the orientation of the cracks and changing the orientation by 5-10 degrees can change the safety factor several times. Enough odnogo adverse combination that basically the ledge collapsed. The analysis of field measurements of cracks and the choice of the most critical combinations is necessary. Also, it is possible to analyze already accomplished collapses (on what systems of cracks they occurred).